(i) Field of the Invention
The present invention relates to a single crystal silicon carbide film as an electronic material, particularly to silicon carbide which is preferable in preparing a semiconductor device and which has a low defect density and to a method for manufacturing the silicon carbide.
(ii) Description of the Related Art
The growth of silicon carbide (SiC) has heretofore been classified to a bulk growth by a sublimation process, and a thin film formation by epitaxial growth onto a substrate.
In the bulk growth by the sublimation process the growth of 6H-SiC or 4H-SiC which is a polytypism with a high temperature phase is possible, and the preparation of SiC itself as the substrate has been realized. However, there are a large number of defects (micro pipes) introduced into a crystal, and it has been difficult to enlarge a substrate area.
On the other hand, when the epitaxial growth process onto a single crystal substrate is used, the enhancement of controllability of impurity addition or the enlargement of substrate area, and the reduction of micro pipes having caused problems in the sublimation process are realized. In the epitaxial growth process, however, the increase of a plane defect density by a difference in lattice constant between a substrate material and a silicon carbide film often raises a problem. Particularly, since Si usually used as the substrate to grow has a large lattice mismatching from SiC, twins and anti phase boundaries (APB) are remarkably generated in an SiC growth layer, and these deteriorate the properties of SiC as an electronic element.
As a method of reducing surface defects in the SiC film, for example, a technique of reducing the surface defects having inherent or more thickness is proposed in Japanese Patent Publication No. 41400/1994, which includes a process of disposing a growth area on a substrate to grow, and a process of allowing a silicon carbide single crystal to grow in this growth area so that its thickness becomes the same as or more than the thickness inherent to the growth surface orientation of the substrate. However, since two orientations of anti phase boundaries contained in SiC have properties to be enlarged in directions orthogonal to each other with respect to the increase of SiC film thickness, the anti phase boundaries cannot effectively be reduced. Furthermore, the direction of a super structure formed on the grown SiC surface cannot arbitrarily be controlled. Therefore, for example, when the separated growth areas are combined with each other according to the growth, the anti phase boundary is newly formed on this combined part, which deteriorates electric properties.
As a method of effectively reducing the anti phase boundaries, K. Shibahara et al. have proposed a growth process onto an Si (100) surface substrate in which a surface normal axis is slightly inclined to [110] from [001] direction (an off angle is introduced) (Upright Physics Letter, vol. 50, 1987, page 1888). In this method, since an atomic level step is introduced at equal intervals in one direction by applying the slight inclination to the substrate, the surface defect having a direction parallel to the introduced step is propagated. On-the other hand, the propagation of the surface defect to the direction vertical to the introduced step (a direction across the step) is effectively suppressed. Therefore, since the anti phase boundary enlarged in the direction parallel to the introduced step is enlarged in preference to the anti phase boundary enlarged in the orthogonal direction in the two orientations of anti phase boundaries included in the film with respect to the film thickness increase of silicon carbide, the anti phase boundaries can effectively be reduced. However, as shown in FIG. 1, in this method, the increase of step density of an SiC/Si interface causes the generation of an undesired anti phase boundary 1, and there is a problem that the anti phase boundary cannot completely be eliminated. Additionally, in FIG. 1, numeral 1 denotes an anti phase boundary generated in the single atom step of Si substrate, 2 denotes an anti phase boundary association point, 3 denotes an anti phase boundary generated in an Si substrate surface terrace, xcex8 denotes an off angle, and xcfx86 denotes an angle (54.7xc2x0) formed between the Si (001) surface and the anti phase boundary. The anti phase boundary 3 generated in the Si substrate surface terrace disappears in the anti phase boundary association point 2, but the anti phase boundary 1 generated in the single atom step of the Si substrate has no other boundary to associate, and does not disappear.
The present invention has been developed under the above-described background, and an object thereof is to provide a silicon carbide film in which anti phase boundaries are effectively reduced or eliminated.
To attain the above-described object, the present invention provides the following constitutions.
(Constitution 1) A method for manufacturing a silicon carbide film in which a crystal orientation is inherited on a single crystal substrate surface and silicon carbide is allowed to epitaxially grow, the method for manufacturing the silicon carbide film comprising the steps of: entirely or partially providing the substrate surface with a plurality of undulations extended parallel in one direction; and allowing silicon carbide to grow on the substrate surface.
(Constitution 2) The method for manufacturing the silicon carbide film in the constitution 1 in which during the growth of the silicon carbide film, an epitaxial growth mechanism is used so that a propagation orientation of a surface defect generated in the film can be limited in a specified crystal surface.
(Constitution 3) The method for manufacturing the silicon carbide film described in the constitution 1 or 2 in which when an average value of an interval between undulation tops of the substrate surface is set to W, the silicon carbide film has a thickness of W/2(=2xc2xd) or more.
(Constitution 4) The method for manufacturing the silicon carbide film described in the constitutions 1 to 3 in which the interval between the undulation tops of the substrate surface is in a range of 0.01 xcexcm to 10 xcexcm, an undulation height difference is in a range of 0.01 xcexcm to 20 xcexcm, and the inclination degree of an inclined surface in the undulation is in a range of 1xc2x0 to 55xc2x0.
(Constitution 5) The method for manufacturing the silicon carbide film described in the constitutions 1 to 4 in which the substrate comprises a single crystal Si, the substrate surface comprises a (001) surface, and the surface is provided with the undulation extended in parallel with a [110] orientation.
(Constitution 6) The method for manufacturing the silicon carbide film described in the constitutions 1 to 4 in which the substrate comprises a single crystal 3C-SiC, the substrate surface comprises a (001) surface, and the surface is provided with the undulation extended in parallel with a [110] orientation.
(Constitution 7) The method for manufacturing the silicon carbide film described in the constitutions 1 to 4 in which the substrate comprises a hexagonal single crystal SiC, the substrate surface comprises a (1, 1, xe2x88x922, 0) surface, and the surface is provided with the undulation extended in parallel with a [1, xe2x88x921, 0, 0] orientation or a [0, 0, 0, 1] orientation.
(Constitution 8) A silicon carbide film manufactured using the method described in the constitutions 1 to 7.
(Constitution 9) The silicon carbide film which comprises a step of a plurality of undulations entirely or partially formed on a single crystal substrate surface and extended parallel in one direction, and which has a structure subjected to epitaxial growth in a method so that a propagation orientation of a film inner surface defect can be limited in a specified crystal surface.
According to the constitution 1, by providing the surface of the substrate to grow of silicon carbide with a plurality of undulations extended parallel in one direction, the effect of introducing the off angle proposed by K. Shibahara et al. can be obtained in the inclined surface of each undulation. Furthermore, in the present invention, since the steps oriented in a Plane symmetrical orientation are introduced to the surface of the substrate to grow of silicon carbide with a statistically balanced density, the anti phase boundaries in the undesirably introduced silicon carbide layer, which generated by the steps on the surface of the substrate, are effectively annihilated, and the silicon carbide film in which the anti phase boundaries are completely eliminated can be obtained. Moreover, in the present invention, the individual growth areas form the same phase area enlarged in the same direction by the off angle introducing effect. Therefore, even when the separated growth areas are combined with one another according to the growth, there is an advantage that no anti phase boundary is produced in the combined part.
Additionally, the undulation mentioned in the present invention does not require a parallel property or a mirror surface symmetrical relation in a mathematically strict meaning, and may have a configuration enough to effectively reduce or eliminate the anti phase boundaries.
Examples of the method of forming an undulation shape on the substrate to grow include a photolithography technique, a press processing technique, a laser processing or ultrasonic processing technique, an abrasion processing technique, and the like. Even when any of the methods is used, the final configuration of the surface of the substrate to grow may have a sufficient configuration to such an extent that the anti phase boundaries can effectively be reduced or eliminated.
When the photolithography technique is used, the arbitrary undulation shape can be transferred to the substrate to grow by arbitrarily forming a mask pattern to be transferred to the substrate. The width of the undulation shape can be controlled, for example, by changing a pattern linear width. Moreover, the depth of the undulation shape or the angle of the inclined surface can be controlled by controlling the etching selection ratio of resist and substrate. Even when a rectangular pattern shape is not required, the undulation pattern with an undulatory shape can be formed by performing a thermal treatment to soften the resist after transferring the pattern to the resist.
When the press processing technique is used, an arbitrary undulation shape can be formed onto the substrate to grow by arbitrarily forming a pressing mold. The undulation with various shapes can be formed on the substrate to grow by forming various shapes of molds.
When the laser or ultrasonic processing technique is used, the undulation shape is directly processed/formed on the substrate, which enables a fine processing.
When the abrasion processing is used, the width or depth of the undulation shape can be controlled by changing the magnitude of abrasive grain diameter or the processing pressure during the abrasion. When the substrate provided with the one-direction undulation shape is prepared, the abrasion is performed only in one direction.
According to the constitution 2, the effect of the constitution 1 can securely and sufficiently be obtained by performing the epitaxial growth under the growth condition so that the propagation orientation of the film inner surface defect can be limited in the specified crystal surface. For example, a step flow growth can satisfy this growth condition.
According to the constitution 3, when the average value of the interval between the undulation tops of the surface of the substrate to grow of silicon carbide is set to W, the silicon carbide film has a thickness of W/2(=2xc2xd). At this time, all the anti phase boundaries disappear. Therefore, it is preferable to set the thickness of the silicon carbide film to W/2(=2xc2xd) or more.
Additionally, to obtain the effect of the present invention with a thin film thickness, the interval between the undulation tops is preferably narrower.
In the constitution 4, the interval of the undulation tops, the undulation height difference, and the inclination degree of the undulation are defined.
The interval of the undulation tops is preferably 0.01 xcexcm or more from the standpoint of the limitation of the fine processing technique in the preparation of the undulation to the substrate to grow. Moreover, when the interval of the undulation tops exceeds 10 xcexcm, the frequency of the association of the anti phase boundaries is excessively lowered. Therefore, the interval of the undulation tops is preferably 10 xcexcm or less. When the undulation top interval is more preferably in a range of 0.1 xcexcm to 3 xcexcm, the effect of the present invention is sufficiently fulfilled.
The height difference and interval of the undulation influence the undulation inclination degree, that is, the step density. Since a preferable step density changes with the crystal growth conditions, this cannot absolutely be said, but the usually necessary undulation height difference has substantially the same degree as the undulation top interval, that is, a range of 0.01 xcexcm to 20 xcexcm.
The effect of the present invention is fulfilled by promoting the growth of silicon carbide in the vicinity of the atomic level step in the surface of the substrate to grow. Therefore, the present invention is realized when the undulation inclination degree is in an inclination of 54.7xc2x0 or less of the (111) surface in which the entire inclined surface is covered with the single step. Moreover, since the undulation inclined surface step density remarkably decreases in the inclination degree less than 1xc2x0, the inclination degree of the undulation inclined surface is preferably 1xc2x0 or more. When the inclination angle of the inclined surface of the undulation is more preferably in a range of 2xc2x0 to 10xc2x0, the effect of the present invention is sufficiently fulfilled.
Additionally, the xe2x80x9cundulation inclined surfacexe2x80x9d mentioned in the present invention includes various configurations such as a flat plane and a curved plane. Moreover, the xe2x80x9cinclination degree of the inclined surface in the undulationxe2x80x9d means the substantial inclination degree of the inclined surface which contributes to the effect of the present invention, and the maximum inclination degree, average inclination degree, and the like can be employed as the xe2x80x9cinclination degree of the undulationxe2x80x9d in accordance with the configuration of the inclined surface.
In the constitutions 5 to 7, the surface orientation of the surface of the substrate to grow of silicon carbide, and the undulation orientation are defined.
When the single crystal Si (001) surface or the cubic silicon carbide (001) surface of the single crystal is used as the surface orientation of the surface of the substrate to grow on which the cubic or hexagonal silicon carbide is allowed to grow, the propagation direction of the anti phase boundary is [110]. Therefore, as shown in FIG. 2, by arranging the undulation of the surface in parallel with any one of the directions ([1, xe2x88x921, 0] direction in FIG. 2), the silicon carbide film can be obtained in which the anti phase boundaries are effectively eliminated on the axis orthogonal to the undulation shown in FIG. 3 (Constitutions 5, 6). Additionally, in FIG. 3, character W denotes the undulation top interval.
When the hexagonal SiC (1, 1, xe2x88x922, 0) surface of the single crystal is used as the surface orientation of the surface of the substrate to grow on which the cubic or hexagonal silicon carbide is allowed to grow, the propagation direction of the anti phase boundary is [1, xe2x88x921, 0, 0], [xe2x88x921, 1, 0, 0], [0, 0, 0, 1], [0, 0, 0, xe2x88x921]. Therefore, by arranging the undulation of the surface in parallel with any one of the directions, the silicon carbide film can be obtained in which the anti phase boundaries are effectively eliminated as described above (Constitution 7).
According to the constitution 8, by using the method described-in the constitutions 1 to 7, the silicon carbide film can be obtained in which the anti phase boundaries are effectively reduced or eliminated.
The silicon carbide film of the present invention has a very superior electric property due to a low crystal boundary density, and can preferably be used as electronic elements such as a semiconductor substrate and a crystal growing substrate (including a seed crystal).
According to the constitution 9, by using the substrate structure and crystal growing method, the silicon carbide film can be obtained in which the anti phase boundaries are effectively reduced or eliminated.